Abstract
Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.
Highlights
Low molecular weight (LMW) thiols, a group of highly reactive compounds containing a sulfhydryl (–SH) functional group, play critical roles within a cell [1]
Even in bacteria that contain glutathione or γ-l-glutamyl-l-cysteinylglycine (GSH), this LMW thiol can be acquired by pathways that differ from the canonical pathway in which GSH is synthesized by the two ligases, γ-glutamate-cysteine ligase (γ-ECL) and glutathione synthetase (GS)
coenzyme A (CoA) has been suggested to be a major thiol in archaea, possibly due to the presence of disulfide reductases (CoADR) that reduce oxidized CoA denoting the ability of these cells to recycle CoA to its reduced form [113,114,115]
Summary
Low molecular weight (LMW) thiols, a group of highly reactive compounds containing a sulfhydryl (–SH) functional group, play critical roles within a cell [1]. (ii) directly donate electrons to oxidants becoming oxidized in the process, forming disulfides (RS-SR) [4,5], (iii) conjugate xenobiotic agents making them more soluble [6], (iv) form complexes with metal ions [7], and (v) act as cofactors to different enzymes, such as ribonucleotide reductases [8] and methionine sulfoxide reductases [9] Because of these roles, LMW thiols are considered ubiquitous among living organisms. Even in bacteria that contain GSH, this LMW thiol can be acquired by pathways that differ from the canonical pathway in which GSH is synthesized by the two ligases, γ-glutamate-cysteine ligase (γ-ECL) and glutathione synthetase (GS) These alternative pathways of GSH acquisition include import [17,18] and the use of a novel fusion protein, GshF, for the biosynthesis of GSH in bacteria that were once thought to lack. This review paper will provide an overview of LMW thiols in prokaryotes with emphasis on the current state of knowledge regarding the distribution and biochemistry of these thiols in archaea
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